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In graph theory, circular coloring may be viewed as a refinement of usual graph coloring. The ''circular chromatic number'' of a graph , denoted can be given by any of the following definitions, all of which are equivalent (for finite graphs). # is the infimum over all real numbers so that there exists a map from to a circle of circumference 1 with the property that any two adjacent vertices map to points at distance along this circle. # is the infimum over all rational numbers so that there exists a map from to the cyclic group with the property that adjacent vertices map to elements at distance apart. #In an oriented graph, declare the ''imbalance'' of a cycle to be divided by the minimum of the number of edges directed clockwise and the number of edges directed counterclockwise. Define the ''imbalance'' of the oriented graph to be the maximum imbalance of a cycle. Now, is the minimum imbalance of an orientation of . It is relatively easy to see that (especially using 1. or 2.), but in fact . It is in this sense that we view circular chromatic number as a refinement of the usual chromatic number. Circular coloring was originally defined by , who called it "star coloring". Coloring is dual to the subject of nowhere-zero flows and indeed, circular coloring has a natural dual notion: circular flows. ==See also== *Rank coloring 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Circular coloring」の詳細全文を読む スポンサード リンク
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